Optical fiber secure communication apparatus and data encrption method therefor

ABSTRACT

An optical fiber secure communication apparatus and a data encryption method therefor are provided. The apparatus comprises a transmitter and a receiver being connected with each other via an optical fiber. The transmitter comprises a PPC processor unit, a field programmable gate array test board, a light-emitting module, an optical fiber coupler and a connection optical fiber. The receiver comprises a wavelength division multiplexer, a connection optical fiber, a photodetector, a field programmable gate array test board, a PPC processor unit and a signal output interface. At the transmitter end, two or more paths of input data are forwarded by the PPC, encrypted by the FPGA and then transmitted to the light-emitting module of two or more wavelengths for conversion from electrical signals into optical signals. At the receiver end, signals of two or more wavelengths enter the photodetector for conversion into electrical signals, which are decrypted by the FPGA and then forwarded by the PPC for output. With the present invention, the security of transmission data is improved and the difficulty in cracking data is increased.

FIELD OF THE INVENTION

The present invention relates to the field of optical fibercommunication technology, and more particularly, to an optical fibersecure communication apparatus and a data encryption method therefor.

BACKGROUND OF THE INVENTION

With development of the communication industry, especially of theoptical communication having broad bandwidth, security of information isof increasing concern. Safety and security have become a chief issue inthe communication industry. Common encryption approaches for the opticalcommunication include information encoding encryption, algorithmencryption, frequency hopping encryption as well as quantum encryptionwhich is recently developed. However, the quantum encryption is, so far,just in the experimental phase and is quite far from commercialapplications.

The concept of frequency hopping encryption originates from the wirelessfrequency hopping communication in which a transmitter continuouslyswitches its carrier wavelength according to a frequency hopping patternand a receiver has to switch its wavelength in the same manner so as toreceive complete information. Also, the interference immunity can beimproved due to continuous switching of the carrier. As the frequencyhopping sequence is randomly generated and thus is irregular, it isdifficult to be cracked.

Currently, the algorithm encryption is commonly employed as oneapplicable to the communication encryption. However, no matter howcomplicated an encryption algorithm is, there is a certain degree ofregularity. Thus, it can be cracked by analyzing the regularity of datavariation.

According to the present invention, the algorithm encryption and thefrequency hopping encryption are combined to provide a novel dataencryption method by which it is possible to encrypt transmission datawithout losing the advantage of broad bandwidth of the opticalcommunication.

SUMMARY OF THE INVENTION Problem to be Solved

A major object of the present invention is to provide an optical fibersecure communication apparatus and a data encryption method therefor, bywhich it is possible to improve the security of transmission data and toincrease the difficulty in cracking the data.

Technical Solution

To achieve the above object, the present invention is made.

According to an aspect of the invention, there is provided an opticalfiber secure communication apparatus, which comprises a transmitter anda receiver being connected with each other via an optical fiber, wherein

the transmitter comprises a first signal input interface, a secondsignal input interface, a first PPC processor unit, a first fieldprogrammable gate array (FPGA) test board, a first semiconductor laser,a second semiconductor laser, a first LiNbO₃ modulator, a second LiNbO₃modulator, a first co-axial transmission line, a second co-axialtransmission line, an optical fiber coupler, a first connection opticalfiber and a second connection optical fiber; wherein the first signalinput interface and the second signal input interface are connected tothe first FPGA test board via the first PPC processor unit; those twopaths of signals are encrypted by the first FPGA test board and thenloaded onto the first LiNbO₃ modulator and the second LiNbO₃ modulatorvia the first co-axial transmission line and the second co-axialtransmission line, respectively; two paths of modulated lights enter theoptical fiber coupler via the first connection optical fiber and thesecond connection optical fiber respectively and are then combined intoone path of output light; the first semiconductor laser and the firstLiNbO₃ modulator as well as the second semiconductor laser and thesecond LiNbO₃ modulator constitute light-emitting modules, respectively;and

the receiver comprises a wavelength division multiplexer, a thirdconnection optical fiber, a fourth connection optical fiber, a firstphotodetector, a second photodetector, a second FPGA test board, asecond PPC processor unit, a first signal output interface and a secondsignal output interface; wherein optical signals are inputted to thewavelength division multiplexer via the optical fiber connecting thetransmitter with the receiver; the optical signals each having arespective wavelength of λ₁ and λ₂ enter the first photodetector and thesecond photodetector via the third connection optical fiber and thefourth connection optical fiber, respectively; two paths of electricalsignals converted by the detectors are decrypted by the second FPGA testboard, forwarded by the second PPC processor unit and then outputted viathe first signal output interface and the second signal output interfacerespectively.

Preferably, the first signal input interface and the second signal inputinterface are each an electrical signal interface or an optical inputinterface; the optical fiber coupler is an optical fiber coupler or amultiple-to-one wavelength division multiplexer; and the first co-axialtransmission line and the second co-axial transmission line are each amicrostrip transmission line directly arranged on a circuit board.

Preferably, the first PPC processor unit and the second PPC processorunit are configured for forwarding data; the first FPGA test board isconfigured for encrypting data; the second FPGA test board is configuredfor decrypting data; the first PPC processor unit and the first FPGAtest board are arranged on a same circuit board, and the second PPCprocessor unit and the second FPGA test board are arranged on a samecircuit board.

Preferably, the light-emitting module comprises a laser and an externalmodulator, or else comprises a DFB laser/EA modulator-integrated lightsource, or else comprises a direct modulation semiconductor laser.

Preferably, the first LiNbO₃ modulator and the second LiNbO₃ modulatoreach further comprise a drive circuit, and optionally a signal levelconversion when the signal level is mismatched.

Preferably, the first semiconductor laser and the second semiconductorlaser are each a wavelength tunable semiconductor laser whose emittingwavelength is controlled by a control circuit of the first FPGA testboard.

Preferably, a 2×2 optical switch is further arranged between the firstsemiconductor laser and the first LiNbO₃ modulator as well as betweenthe second semiconductor laser and the second LiNbO₃ modulator, which isconfigured to switch signals under control of a control circuit of thefirst FPGA test board.

Preferably, the wavelength division multiplexer is a Mach-Zehnderinterferometer filter composed of two 3 dB optical fiber couplers.

Preferably, at the transmitter, two or more paths of input data areforwarded by the first PPC processor unit, encrypted by the first FPGAtest board and then transmitted to the light-emitting modules of two ormore wavelengths for conversion from electrical signals into opticalsignals.

Preferably, at the receiver, signals of two or more wavelengths enterthe first photodetector and the second photodetector, respectively, forconversion into electrical signals, which are decrypted by the secondFPGA test board and then forwarded by the second PPC processor unit tobe outputted.

According to a further aspect of the invention, there is provided a dataencryption method for an optical fiber secure communication apparatus isprovided, which comprises steps of:

pre-framing service data and performing algorithm encryption on theservice data in a unit of group comprising a plurality of frames, thenumber of frames in each group being dependent on a security level;

re-framing the encrypted service data and interchanging the framed dataamong different signal paths according to a frequency hopping sequence;

delaying the respective paths of data differently to perform dataencryption; and

modulating the encrypted data at a transmitter of the optical fibersecure communication apparatus.

Preferably, the step of interchanging the framed data according to thefrequency hopping sequence is achieved by an optical switch.

ADVANTAGEOUS EFFECTS

It can be seen from the above that the present invention has thefollowing advantageous effects.

1) With the optical fiber secure communication apparatus according tothe present invention, the transmitter interchanges the input databetween the two paths in a unit of frame according to a frequencyhopping sequence. Thus, a cracker has to obtain the both paths ofsignals and know the frequency hopping sequence and exact frameidentifications in order to continuously recover the frame data.

2) With the optical fiber secure communication apparatus according tothe present invention, the transmitter pre-frames the service data andperforms algorithm encryption on the service data in a unit of groupcomprising a plurality of frames before interchanging the data frames.Thus, even if a cracker knows the encryption algorithm and the frameidentifications, the cracker has to obtain the complete frame data inorder to recover the original information segment for obtaining theactual information. As an example, for 100 frames of data, a crackerwithout the knowledge about the frequency hopping sequence will have totry 2¹⁰⁰ (about 10³⁰) times before obtaining a segment of usefulinformation, which is nearly an impossible task.

3) With the optical fiber secure communication apparatus according tothe present invention, non-service data such as synchronizationinformation and frame identifications are scrambled at the transmitteraccording to the data encryption scheme, such that it is more difficultfor a cracker to crack the frame identifications.

4) In the transmitter of the optical fiber secure communicationapparatus according to the present invention, an additional wavelengthencoding may be provided by replacing the common semiconductor laserwith a tunable semiconductor laser, thereby increasing the difficulty inintercepting and cracking information.

BRIEF DESCRIPTION OF DRAWINGS

For further illustration of the present invention, embodiments of thepresent invention will be described in detail in the following withreference to the drawings, in which:

FIG. 1 is a structural diagram showing an optical fiber securecommunication apparatus according to an embodiment of the presentinvention;

FIG. 2 is a flowchart showing data encryption and decryption method forthe optical fiber secure communication apparatus according to anembodiment of the present invention; and

FIG. 3 is a structural diagram showing the optical fiber securecommunication apparatus with a transmitter into which a 2×2 opticalswitch is added according to an embodiment of the present invention.

REFERENCE NUMERALS

-   -   1, 2 signal input interface    -   3 PowerPC (PPC) processor unit    -   4 field programmable gate array (FPGA) test board    -   5, 6 semiconductor laser    -   7, 8 LiNbO₃ modulator    -   9, 10 co-axial transmission line    -   11, 12 connection optical fiber    -   13 1×2 optical fiber coupler    -   14 transmitter    -   15 wavelength division multiplexer    -   16, 17 connection optical fiber    -   18, 19 photodetector    -   20 field programmable gate array (FPGA) test board    -   21 PPC processor unit    -   22, 23 signal output interface    -   24 receiver    -   25 connection optical fiber

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will be further described in detail in thefollowing in conjunction with embodiments thereof with reference to thedrawings, so that the above and other objects, features and advantagesof the present invention become more apparent.

The present invention borrows the concept of the wireless frequencyhopping communication in combination with the algorithm encryption, toachieve signal encryption by alternately loading signals on twodifferent optical wavelengths according to a frequency hopping sequenceand also scrambling data based on a certain algorithm.

FIG. 1 is a structural diagram showing an optical fiber securecommunication apparatus according to an embodiment of the presentinvention. As shown in FIG. 1, the apparatus comprises a transmitter 14and a receiver 24 being connected with each other via an optical fiber25, wherein

the transmitter 14 comprises a first signal input interface 1, a secondsignal input interface 2, a first PowerPC (PPC) processor unit 3, afirst field programmable gate array (FPGA) test board 4, a firstsemiconductor laser 5, a second semiconductor laser 6, a first LiNbO₃modulator 7, a second LiNbO₃ modulator 8, a first co-axial transmissionline 9, a second co-axial transmission line 10, an optical fiber coupler13, a first connection optical fiber 11 and a second connection opticalfiber 12; wherein the first signal input interface 1 and the secondsignal input interface 2 are connected to the first FPGA test board 4via the first PPC processor unit 3; those two paths of signals areencrypted by the first FPGA test board 4 and then loaded onto the firstLiNbO₃ modulator 7 and the second LiNbO₃ modulator 8 via the firstco-axial transmission line 9 and the second co-axial transmission line10, respectively; two paths of modulated lights enter the optical fibercoupler 13 via the first connection optical fiber 11 and the secondconnection optical fiber 12 respectively and are then combined into onepath of output light; the first semiconductor laser 5 and the firstLiNbO₃ modulator 7 as well as the second semiconductor laser 6 and thesecond LiNbO₃ modulator 8 constitute light-emitting modules,respectively; and

the receiver 24 comprises a wavelength division multiplexer 15, a thirdconnection optical fiber 16, a fourth connection optical fiber 17, afirst photodetector 18, a second photodetector 19, a second FPGA testboard 20, a second PPC processor unit 21, a first signal outputinterface 22 and a second signal output interface 23; wherein opticalsignals are inputted to the wavelength division multiplexer 15 via theoptical fiber 25 connecting the transmitter 14 with the receiver 24; theoptical signals each having a respective wavelength of λ₁ and λ₂ enterthe first photodetector 18 and the second photodetector 19 via the thirdconnection optical fiber 16 and the fourth connection optical fiber 17,respectively; two paths of electrical signals converted by the detectorsare decrypted by the second FPGA test board 20, forwarded by the secondPPC processor unit 21 and then outputted via the first signal outputinterface 22 and the second signal output interface 23 respectively.

Although there are two paths of signals inputted to the transmitter asdescribed above, the present invention is not limited thereto and theremay be two or more paths of input signals. While the first signal inputinterface 1 and the second signal input interface 2 as described aboveare electrical signal interfaces (such as general network interfaces),they may be optical input interfaces. The optical fiber coupler 13 is anoptical fiber coupler, or otherwise it may be a multiple-to-onewavelength multiplexer, i.e., it may be replaced with a multiple-to-onewavelength multiplexer. Further, the first co-axial transmission line 9and the second co-axial transmission line 10 are each a microstriptransmission line directly arranged on a circuit board.

The first PPC processor unit 3 and the second PPC processor unit 21 areconfigured for forwarding data; the first FPGA test board 4 isconfigured for encrypting data; the second FPGA test board 20 isconfigured for decrypting data; the first PPC processor unit 3 and thefirst FPGA test board 4 are arranged on one same circuit board, and thesecond PPC processor unit 21 and the second FPGA test board 20 arearranged on one same circuit board.

The light-emitting module comprises a laser and an external modulator,or else comprises a DFB laser/EA modulator-integrated light source, orelse comprises a direct modulation semiconductor laser.

The first LiNbO₃ modulator 7 and the second LiNbO₃ modulator 8 eachfurther comprise a drive circuit, and optionally a signal levelconversion when the signal level is mismatched.

The first semiconductor laser 5 and the second semiconductor laser 6 areeach a wavelength tunable semiconductor laser whose emitting wavelengthis controlled by a control circuit of the first FPGA test board 4.

A 2×2 optical switch is further arranged between the first semiconductorlaser 5 and the first LiNbO3 modulator 7 as well as between the secondsemiconductor laser 6 and the second LiNbO3 modulator 8, which isconfigured to switch signals under control of a control circuit of thefirst FPGA test board 4, as illustrated in FIG. 3.

The wavelength division multiplexer 15 is a Mach-Zehnder interferometerfilter composed of two 3 dB optical fiber couplers.

The optical fiber coupler 13, the first connection optical fiber 11, thesecond connection optical fiber 12 as well as the wavelength divisionmultiplexer 15, the third connection optical fiber 16 and the fourthconnection optical fiber 17 may be replaced with free-space optical pathdevices.

FIG. 2 is a flowchart showing a data encryption and decryption methodfor the optical fiber secure communication apparatus as shown in FIG. 1according to an embodiment of the invention. Herein, FIG. 2 a is aflowchart showing the data encryption method for the optical fibersecure communication apparatus, and FIG. 2 b is a flowchart showing thedata decryption method for the optical fiber secure communicationapparatus.

As shown in FIG. 2 a, the data encryption method for the optical fibersecure communication apparatus according to the embodiment of thepresent invention comprises steps of: pre-framing service data andperforming algorithm encryption on the service data in a unit of groupcomprising a plurality of frames, the number of frames in each groupbeing dependent on a security level; re-framing the encrypted servicedata and interchanging the framed data among different signal pathsaccording to a frequency hopping sequence; delaying the respective pathsof data differently to perform data encryption; and modulating theencrypted data at the transmitter of the optical fiber securecommunication apparatus. Herein, the step of interchanging the frameddata among the different paths according to the frequency hoppingsequence is achieved by the optical switch.

As shown in FIG. 2 b, the data decryption method for the optical fibersecure communication apparatus according to the embodiment of thepresent invention is an inverse operation of the encryption.

Herein, the data encryption and decryption are both performed by FPGAfunctional modules, where input data is subject to pre-framing,algorithm encrypting, re-framing and interchanging according to thefrequency hopping sequence, so as to be encrypted.

At the transmitter end, two or more paths of input data are forwarded bythe first PPC processor unit 3, encrypted by the first FPGA test board 4and then transmitted to the light-emitting modules of two or morewavelengths for conversion from electrical signals into optical signals.

At the receiver end, signals of two or more wavelengths enter the firstphotodetector 18 and the second photodetector 19, respectively, forconversion into electrical signals, which are decrypted by the secondFPGA test board 20 and then forwarded by the second PPC processor unit21 to be outputted.

The objects, features and advantageous effects of the present inventionhave been described in detail with respect to the above embodiments. Itshould be understood that the above description is only illustration ofthe particular embodiments of the present invention, rather thanlimitation of the invention. Therefore, modifications, equivalentalternatives and improvements may be made without departing from thespirits and principles of the present invention, which all fall into thescope of the present invention.

1. An optical fiber secure communication apparatus, comprising atransmitter (14) and a receiver (24) being connected with each other viaan optical fiber (25), wherein the transmitter (14) comprises a firstsignal input interface (1), a second signal input interface (2), a firstPPC processor unit (3), a first field programmable gate array (FPGA)test board (4), a first semiconductor laser (5), a second semiconductorlaser (6), a first LiNbO₃ modulator (7), a second LiNbO₃ modulator (8),a first co-axial transmission line (9), a second co-axial transmissionline (10), an optical fiber coupler (13), a first connection opticalfiber (11) and a second connection optical fiber (12); wherein the firstsignal input interface (1) and the second signal input interface (2) areconnected to the first FPGA test board (4) via the first PPC processorunit (3); those two paths of signals are encrypted by the first FPGAtest board (4) and then loaded onto the first LiNbO₃ modulator (7) andthe second LiNbO₃ modulator (8) via the first co-axial transmission line(9) and the second co-axial transmission line (10), respectively; twopaths of modulated lights enter the optical fiber coupler (13) via thefirst connection optical fiber (11) and the second connection opticalfiber (12) respectively and are then combined into one path of outputlight; the first semiconductor laser (5) and the first LiNbO₃ modulator(7) as well as the second semiconductor laser (6) and the second LiNbO₃modulator (8) constitute light-emitting modules, respectively; and thereceiver (24) comprises a wavelength division multiplexer (15), a thirdconnection optical fiber (16), a fourth connection optical fiber (17), afirst photodetector (18), a second photodetector (19), a second FPGAtest board (20), a second PPC processor unit (21), a first signal outputinterface (22) and a second signal output interface (23); whereinoptical signals are inputted to the wavelength division multiplexer (15)via the optical fiber (25) connecting the transmitter (14) with thereceiver (24); the optical signals each having a respective wavelengthof λ₁ and λ₂ enter the first photodetector (18) and the secondphotodetector (19) via the third connection optical fiber (16) and thefourth connection optical fiber (17), respectively; two paths ofelectrical signals converted by the detectors are decrypted by thesecond FPGA test board (20), forwarded by the second PPC processor unit(21) and then outputted via the first signal output interface (22) andthe second signal output interface (23) respectively.
 2. The opticalfiber secure communication apparatus according to claim 1, wherein thefirst signal input interface (1) and the second signal input interface(2) are each an electrical signal interface or an optical inputinterface; the optical fiber to coupler (13) is an optical fiber coupleror a multiple-to-one wavelength division multiplexer; and the firstco-axial transmission line (9) and the second co-axial transmission line(10) are each a microstrip transmission line directly arranged on acircuit board.
 3. The optical fiber secure communication apparatusaccording to claim 1, wherein the first PPC processor unit (3) and thesecond PPC processor unit (21) are configured for forwarding data; thefirst FPGA test board (4) is configured for encrypting data; the secondFPGA test board (20) is configured for decrypting data; the first PPCprocessor unit (3) and the first FPGA test board (4) are arranged on asame circuit board, and the second PPC processor unit (21) and thesecond FPGA test board (20) are arranged on a same circuit board.
 4. Theoptical fiber secure communication apparatus according to claim 1,wherein the light-emitting module comprises a laser and an externalmodulator, or else comprises a DFB laser/EA modulator-integrated lightsource, or else comprises a direct modulation semiconductor laser. 5.The optical fiber secure communication apparatus according to claim 1,wherein the first LiNbO₃ modulator (7) and the second LiNbO₃ modulator(8) each further comprise a drive circuit, and optionally a signal levelconversion when the signal level is mismatched.
 6. The optical fibersecure communication apparatus according to claim 1, wherein the firstsemiconductor laser (5) and the second semiconductor laser (6) are eacha wavelength tunable semiconductor laser whose emitting wavelength iscontrolled by a control circuit of the first FPGA test board (4).
 7. Theoptical fiber secure communication apparatus according to claim 1,wherein a 2×2 optical switch is further arranged between the firstsemiconductor laser (5) and the first LiNbO₃ modulator (7) as well asbetween the second semiconductor laser (6) and the second LiNbO₃modulator (8), which is configured to switch signals under control of acontrol circuit of the first FPGA test board (4).
 8. The optical fibersecure communication apparatus according to claim 1, wherein thewavelength division multiplexer (15) is a Mach-Zehnder interferometerfilter composed of two 3 dB optical fiber couplers.
 9. The optical fibersecure communication apparatus according to claim 1, wherein at thetransmitter (14), two or more paths of input data are forwarded by thefirst PPC processor unit (3), encrypted by the first FPGA test board (4)and then transmitted to the light-emitting modules of two or morewavelengths for conversion from electrical signals into optical signals.10. The optical fiber secure communication apparatus according to claim1, wherein at the receiver (24), signals of two or more wavelengthsenter the first photodetector (18) and the second photodetector (19),respectively, for conversion into electrical signals, which aredecrypted by the second FPGA test board (20) and then forwarded by thesecond PPC processor unit (21) to be outputted.
 11. A data encryptionmethod for an optical fiber secure communication apparatus, comprisingsteps of: pre-framing service data and performing algorithm encryptionon the service data in a unit of group comprising a plurality of frames,the number of frames in each group being dependent on a security level;re-framing the encrypted service data and interchanging the framed dataamong different signal paths according to a frequency hopping sequence;delaying the respective paths of data differently to perform dataencryption; and modulating the encrypted data at a transmitter of theoptical fiber secure communication apparatus.
 12. The data encryptionmethod for the optical fiber secure communication apparatus according toclaim 11, wherein the step of interchanging the framed data according tothe frequency hopping sequence is achieved by an optical switch.